A two-dimensional organic LED array for image manifestation apparatus applications is composed of a plurality of organic LEDs (one or more of which form a pixel) arranged in rows and columns. Each individual organic LED in the array is generally constructed with a light transmissive first electrode, an organic electroluminescent medium deposited on the first electrode, and a metallic electrode on top of the organic electroluminescent medium. The electrodes of the LEDs are connected to form a two-dimensional X-Y addressing pattern. In practice, the X-Y addressing pattern is achieved by patterning the light transmissive electrodes in an X direction and patterning the metallic electrodes in a Y direction (or vice versa if desired), with the X and Y directions being perpendicular to each other. The patterning of the electrodes is usually accomplished by either shadow mask or etching techniques. Due to the technical limits of shadow masks, only etching processes are being utilized for high density information displays, which have pixel pitches less then 0.1 mm.
Depending on the medium used in the etching processes, the etching technique can be divided into two categories: wet and dry. While wet etching is performed in an acidic liquid medium, dry etching is usually done in a plasma atmosphere.
The metallic electrodes used for cathode contacts in organic LEDs usually contain a stable metal and a highly reactive metal with a work function less then 4 eV. The presence of the highly reactive metal in the metallic electrode makes acid-based wet etching undesirable. However, the dry etching processes is also problematic because of the high temperature (&gt;200.degree. C. ) and reactive ion atmosphere required in the process, which may affect the integrity of the organic materials as well as the active metal containing metallic electrodes in a two-dimensional organic LED array.
To overcome the etching dilemma, a shadow wall method to fabricate the two-dimensional array has been disclosed by Tang in a patent application, EP92 122113.1, published by the European Patent Office on Jul. 7, 1993. The shadow wall method includes: patterning the transparent electrode first; building dielectric walls that are orthogonal to the transparent electrodes, capable of shadowing an adjacent pixel area, and with a height exceeding the thickness of the organic medium; depositing an organic electroluminescent medium; and depositing the cathode metals from an angle of 15.degree. to 45.degree. with respect to the deposition surface. Since the height of the dielectric walls exceeds the thickness of the organic medium, isolated parallel metal stripes are formed. Thus, a X-Y addressable array is achieved without the need of metal etching. Though this method seems to be viable for metal patterning, it is limited to certain pitch dimensions, and potentially could introduce defects in pixels in the array.
Accordingly, it would be highly advantageous to provide a new LED array and method of manufacturing which overcame these problems.
It is a purpose of this invention to provide a novel method of fabricating a two-dimensional organic LED array for high density information image manifestation apparatus applications.
It is another purpose of this invention to provide an organic LED device structure on which metal etching can be performed.
It is still another purpose of this invention to provide a passivated two-dimensional organic LED array for high density information image manifestation apparatus applications with improved reliability.
It is a further purpose of this invention to provide a new device structure for use in LED arrays which is relatively easy and inexpensive to manufacture.